1. Field of the Invention
The present invention relates to an exposure apparatus for selectively exposing the peripheral portion of a circular substrate such as a wafer for integrated circuit manufacturing purposes.
2. Description of the Prior Art
The manufacture of semiconductor devices has heretofore involved a problem that the resist applied to the surface of a silicon wafer or substrate to form a fine pattern therein tends to be peeled off particularly in the peripheral portion of the wafer during the transfer and other handling operations of the wafer within a semiconductor manufacturing apparatus and such peeled-off resist pieces give rise to various ill effects during the subsequent integrated circuit manufacturing operations.
In order to prevent peeling off of the resist in the peripheral portion of a wafer, it has been the practice in the past to selectively expose only the peripheral edge of the wafer to light by a special-purpose exposure apparatus to cure the resist. This conventional technique has been such that the exposure light beam is projected from a fixed position onto the peripheral portion of the wafer which is rotated in a plane and therefore it is impossible to accurately control the width of an exposure area in the wafer peripheral portion along the whole circumference of the wafer.
In other words, the ordinary wafer is formed in a part of its substantially circular outer periphery with a flat cut-off portion which is called as an orientation flat portion (hereinafter simply referred to as an OF portion) and adapted to determine the orientation of the wafer. Thus, there is a disadvantage that for instance, the width of an exposure area of the wafer peripheral portion is varied due to the tolerance for the outer diameter of the wafer, variation in the position at which the wafer is held and rotated and so on so that particularly when the cut-off at the OF portion 2a of the wafer 2 is large, the exposure area 2b is interrupted near the central portion of the OF portion 2a as shown in FIG. 6a or alternatively to ensure the exposure of the perpheral portion along the whole circumference without any interruption requires that the exposure area 2b of the peripheral portion is widened considerably as shown in FIG. 6b.
There is another disadvantage that conventially the exposure light beam on the wafer perpheral portion has such a sectional shape that it forms a simple circular spot S as shown in FIG. 7a so that as shown in FIG. 7b, the integrated exposure light quantity P in the wafer peripheral portion is not uniform over the wafer radial distance D from the wafer edge position E so that if the spot is displaced in the wafer radial direction relative to the wafer, variation in the integrated exposure light quantity is caused and it is impossible to ensure uniform exposure of the peripheral portion of the wafer along its whole circumference with the minimum required exposure light quantity.
There is still another disadvantage that where the exposure of a wafer peripheral portion is effected by a special-purpose exposure apparatus provided independently of the main exposure apparatus provided essentially for the exposure of the pattern contained in a mask or an exposure apparatus incorporated in a resist coating equipment or resist developing equipment, it is difficult to utilize the data relating to the proper exposure light quantity already stored in the main exposure apparatus provided essentially for the exposure of the mask pattern in connection with the resist used, and consequently it is impossible to effect the proper exposure unless the exposure light quantity data for the peripheral portion exposure are separately administered.